What should I do with my old laptop in 2026?

Give it to someone you know who needs a laptop.

Hang on to it if it still works, and you've got a power supply. There's going to be disruptions to global trade one way or the other (Trump does insane things, OR Xi invades Taiwan) that will completely mess up the availability of CPUs, and indeed, most electronics. You may be able to sell it for a profit, or be in the top percent of computer owners in 3 years.

Setup Proxmox and Tailscale on it so you can create VMs or containers as you need and access them from anywhere.

Setup Coolify on it. With Coolify and Cloudflare Tunnels you can self host your personal projects even behind CG-NAT.